Magnetic data carriers make use of the ferromagnetism phenomenon for storing data. Recording and reading of data take place with the use of disk read-and-write heads. The examples of magnetic data carriers are a hard disk platter or a drum memory.
The method according to the invention can be very well applied for destroying of hard disk platters (computer magnetic disks), as it eliminates completely and irretrievably magnetic data carriers together with the data recorded thereon, and thus disables re-reading the data at a later time.
A computer hard disk comprises a hard structure (a hard disk casing) containing a drive unit, read and write circuits, controlling systems and from one to a few platters.
Hard disk platters, on which data is recorded, are usually made of aluminum or its alloys with magnesium and both their sides are covered with a very thin, polished layer with ferromagnetic properties. The alloys used in the production of ferromagnetic layers are alloys of elements such as Fe, Ni, Cr, Co, and optionally Nb, B, Si, Ta and others. Ferromagnetic layers are usually coated with a protecting layer, typically a protective layer of varnish.
In the state of the art, there are known and applied software data erasing methods involving multiple overwriting of sectors that include information with random number sequences. The software data erasing method includes the use of specially designed application for data erasing and the data carrier being in working order is a condition for the effectiveness of this method. Operation of data erasing software involves overwriting of data that is to be erased. As a result of the information overwriting, the data is permanently erased from the data carrier. The re-reading thereof is impossible even in specialist data retrieval laboratories. Each disk undergoes data erasing in a few cycles, techniques applying even up to 35 cycles of overwriting are employed.
There are also known and applied methods for physical destroying of data recorded on computer data carriers; they include scraping off the active layer, i.e. the layer responsible for data storing, from the data carrier surface. This method is employed in a device known from the Japanese patent application No. JP 2004-326997, in which a knife blade is directed onto the surface of the disk and after the pressure is activated, the blade cuts the overlay together with the protective and reflexive layer.
There are also known methods for thermal destroying of data carriers, e.g. methods using electromagnetic waves, such as microwaves. The U.S. patent application No. US 2004/0126450 describes the use of electromagnetic radiation in destroying data recorded on a device, which contains a data storage region and a transmitting region. The method described in this document involves destroying that applies electromagnetic radiation, such as microwave radiation, that induces the electric current flow in the transmitting layer of the disk in the storage data device. The produced heat causes a change in the physical properties of parts of the data storage region of the disk.
The U.S. patent application No. US 2001/0002297 describes a method for destroying of data carrier, e.g. a memory disk equipped with a pyrotechnical layer, wherein the pyrotechnical layer is detonated in order to destroy the data recorded on the data carrier. According to this method, the detonation is initiated with an electric igniter.
Other known methods involve crushing of a disk memory unit with a built-in data carrier in the form of a hard disk, as it was described in the Japanese patent application No. JP 2005-085412, wherein the device with the hard disk is crushed with its base by a pressure unit and the magnetic disk in the device being destroyed is deformed in such a way that the data recorded is impossible to be read.
Another known method for destroying data on hard disks is a chemical method. This method is employed in a system described in the international publication of patent application WO 2004/084470, the system is used to disable reading of the data stored on the data carriers and it involves the use of containers with reactant chemicals or an aerosol container. The U.S. patent application No. US 2005/0257049 describes a chemical substance used for disabling reading of data from a magnetic data carrier that has the following composition: cerium ammonium nitrate in the quantity of 2 to 20% by weight, hydrochloric acid in the quantity of 1.8 to 10% by weight, and water. German utility model application No. DE 20 2005 002 351 U1 describes a device used for erasing information, in which the data carrier is subjected to mechanical means and an acid or an alkaline solution that irretrievably chemically etches the surface of the data carrier.
Polish patent application No. P.381805 [PL381805] describes a two stage method for complete chemical destroying of data carriers. In the first stage, the aluminum layer of the hard disk platters is dissolved with the use of sodium hydroxide aqueous solution with concentration of 20 to 50% by weight, or hydrochloric acid aqueous solution with concentration of 10 to 36% by weight, or sulphuric(VI) acid aqueous solution with concentration of 10 to 60% by weight. In the second stage, the ferromagnetic layer, remaining after the first stage, is dissolved with the use of aqua regia. The disadvantage of this method consists in that it is conducted in two separate reactors, and two different aqueous solutions are obtained as final products thereof, and thus they have to be separately channeled to a sewage treatment plant in order to utilize them.